Floating the 'scope
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From: George Herold on 5 Mar 2010 22:05 Why do they make 'scope inputs ground referenced to the third wire of the AC plug? Today I smoked the 10 ohm resistor that was separating The AC ground from the 'ground' of my circuit. I'd forgotten to float the 'scope and connected -15V to the ground clip of the scope probe. George H.
From: Phil Allison on 5 Mar 2010 22:10 "George Hairoil" > Why do they make 'scope inputs ground referenced to the third wire of > the AC plug? ** For obvious safety reasons. It helps reduce the number of technicians getting electrocuted. But YOU go right ahead and float yours - by all means. ..... Phil
From: John Larkin on 5 Mar 2010 22:38 On Fri, 5 Mar 2010 19:05:54 -0800 (PST), George Herold <ggherold(a)gmail.com> wrote: >Why do they make 'scope inputs ground referenced to the third wire of >the AC plug? Today I smoked the 10 ohm resistor that was separating >The AC ground from the 'ground' of my circuit. I'd forgotten to float >the 'scope and connected -15V to the ground clip of the scope probe. > >George H. That's a safety thing. Our TPS2024 has four truly floating channels and floating trigger input. You can hook a scope ground clip anywhere. John
From: George Herold on 5 Mar 2010 22:41 On Mar 5, 10:10 pm, "Phil Allison" <phi...(a)tpg.com.au> wrote: > "George Hairoil" > > > Why do they make 'scope inputs ground referenced to the third wire of > > the AC plug? > > ** For obvious safety reasons. > > It helps reduce the number of technicians getting electrocuted. > > But YOU go right ahead and float yours - by all means. > > .... Phil Hi Phil, now don't yell at me too much, it's Friday night here and I'm half in the bag. I've been floating 'scopes for.... say since the early '80's. I haven't been biten by it yet. (Though I've made plenty of other mistakes.) What are the obvious safety reasons? In today's mistake I was looking at the voltage from a heater circuit. The heater runs off +15 and -15 but knows 'nothing' about ground. (Well nothing except for the bypass caps, but no DC connection.) Things weren't quite working right and I worried about some oscillation. I hooked up the 'scope to look.... opps. George H. (who believes that you make progress only as fast as you can make mistakes...)
From: Phil Allison on 5 Mar 2010 22:49
"George Hairoil" I've been floating 'scopes for.... say since the early '80's. I haven't been biten by it yet. (Though I've made plenty of other mistakes.) What are the obvious safety reasons? ** My god you are stupid. ..... Phil |